NCERT Class 9 Maths Solutions Chapter - 4 Linear Equations in Two Variables, Ex - 4.1

Ex - 4.1

Question 1.  The cost of a notebook is twice the cost of a pen. Write a linear equation in two variables to represent this statement.

Solution

Let cost of notebook and a pen be x and y respectively.

Cost of note book = 2  cost of pen
              x = 2y
      x - 2 y = 0 

Question 2.  Express the following linear equations in the form ax + by + c = 0 and indicate the values of a, b c in each case:

(i) 

(ii)  

(iii) -2x + 3y = 6 

(iv) x = 3y 

(v) 2x = -5y 

(vi) 3x + 2 = 0 

(vii) y - 2 = 0

(viii) 5 = 2x

Solution

(i) 

     Comparing this equation with ax + by + c = 0

      

(ii) 

       Comparing this equation with ax + by + c = 0

       a = 1, b = - , c = -10

(iii)  - 2x + 3 y = 6
       - 2x + 3 y - 6 = 0

       Comparing this equation with ax + by + c = 0
       a = - 2, b = 3, c = -  6   

(iv)  x = 3y
       1x - 3y + 0 = 0
       Comparing this equation with ax + by + c = 0
       a = 1, b = - 3, c = 0

(v)  2x = - 5y
      2x + 5y + 0 = 0  

      Comparing this equation with ax + by + c = 0
      a = 2, b = 5, c = 0

(vi)  3x + 2 = 0
       3x + 0.y + 2 = 0

        Comparing this equation with ax + by + c = 0
        a = 3, b = 0, c = 2

(vii)  y - 2 = 0
        0.x + 1.y - 2 = 0  

        Comparing this equation with ax + by + c = 0
        a = 0, b = 1, c = - 2

(viii)  5 = 2x
         - 2x + 0.y + 5 = 0
        Company this equation with ax + by + c = 0
        a = - 2, b = 0, c = 5

Ex-4.2